Thermodynamic parameters in the Earth as determined from seismic profiles

Brown, J. M.; Shankland, T. J.

doi:10.1111/j.1365-246x.1981.tb04891.x

Cited by 557 publications

(460 citation statements)

References 40 publications

(24 reference statements)

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“…Along an adiabatic geotherm (26), spin crossovers manifest most strongly near 75 GPa (∼1,750-km depth) in a pyrolitic mantle (Fig. S2).…”

Section: Resultsmentioning

confidence: 99%

“…2B caption) implies that a lateral temperature change of ΔT l ∼ ± 500 K manifests at ∼1,100-km depth or between ∼2,350-and 2,620-km depths as ΔV P ∼ 1%, whereas between 1,650 and 1,800 km it produces ΔV P ∼ 0:3%. For a pyrolitic mantle with 18 wt % of Mg 0:81 Fe 0:19 O, ΔV P ∼ 0% at 73 GPa (∼1,720 km) along the adiabatic geotherm (26). Along the superadiabatic geotherm (27), ΔV P ∼ 0% at 78 GPa (∼1,820 km) for a mantle with 21 wt % of Mg 0:81 Fe 0:19 O.…”

Section: Significancementioning

confidence: 96%

“…The effect of the spin crossover in Fp on the elastic modulus of uniform aggregates with pyrolitic composition (1) was estimated along likely mantle geotherms (26,27). Variations in mineral and aggregate compositions were investigated to estimate uncertainties in predicted effects of Fp on heterogeneities and their ratios (Figs.…”

Section: Methodsmentioning

confidence: 99%

“…4). Along plausible mantle geotherms (26,27) and for several homogeneous aggregates, R S=P is insensitive to composition outside the spin crossover zone, i.e., above 1,200-km depth (Fig. 4).…”

Section: Significancementioning

confidence: 99%

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Spin crossover in ferropericlase and velocity heterogeneities in the lower mantle

Wentzcovitch

2014

Proc. Natl. Acad. Sci. U.S.A.

109

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Deciphering the origin of seismic velocity heterogeneities in the mantle is crucial to understanding internal structures and processes at work in the Earth. The spin crossover in iron in ferropericlase (Fp), the second most abundant phase in the lower mantle, introduces unfamiliar effects on seismic velocities. Firstprinciples calculations indicate that anticorrelation between shear velocity (V S ) and bulk sound velocity (V φ ) in the mantle, usually interpreted as compositional heterogeneity, can also be produced in homogeneous aggregates containing Fp. The spin crossover also suppresses thermally induced heterogeneity in longitudinal velocity (V P ) at certain depths but not in V S . This effect is observed in tomography models at conditions where the spin crossover in Fp is expected in the lower mantle. In addition, the one-of-a-kind signature of this spin crossover in the R S/P (∂ ln V S =∂ ln V P ) heterogeneity ratio might be a useful fingerprint to detect the presence of Fp in the lower mantle.seismic tomography | lateral heterogeneity | elastic modulus | density functional theory | mantle plume F erropericlase (Fp) is believed to be the second most abundant phase in the lower mantle (1, 2). Since the discovery of the high-spin (HS) to low-spin (LS) crossover in iron in Fp (3), this phenomenon has been investigated extensively experimentally and theoretically (4-14). Most of its properties are affected by the spin crossover. In particular, thermodynamics (14) and thermal elastic properties (15)(16)(17)(18)(19)(20) are modified in unusual ways that can change profoundly our understanding of the Earth's mantle. However, this is a broad and smooth crossover that takes place throughout most of the lower mantle and might not produce obvious signatures in radial velocity or density profiles (20, 21) (see Figs. S1 and S2). Therefore, its effects on aggregates are more elusive and indirect. For instance, the associated density anomaly can invigorate convection, as demonstrated by geodynamics simulations in a homogeneous mantle (22)(23)(24). The bulk modulus anomaly may decrease creep activation parameters and lower mantle viscosity (10, 24, 25) promoting mantle homogenization in the spin crossover region (24), and anomalies in elastic coefficients can enhance anisotropy in the lower mantle (16). Less understood are its effects on seismic velocities produced by lateral temperature variations.The present analysis is based on our understanding of thermal elastic anomalies caused by the spin crossover. It has been challenging for both experiments (15-19) and theory (20) to reach a consensus on this topic. Measurements often seemed to include extrinsic effects, making it difficult to confirm the spin crossover signature by different techniques and across laboratories. A theoretical framework had to be developed to address these effects. However, an agreeable interpretation of data and results has emerged recently (20). With increasing pressure, nontrivial behavior is observed in all elastic coefficients, aggregate mo...

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“…Along an adiabatic geotherm (26), spin crossovers manifest most strongly near 75 GPa (∼1,750-km depth) in a pyrolitic mantle (Fig. S2).…”

Section: Resultsmentioning

confidence: 99%

Section: Significancementioning

confidence: 96%

Section: Methodsmentioning

confidence: 99%

Section: Significancementioning

confidence: 99%

See 2 more Smart Citations

Spin crossover in ferropericlase and velocity heterogeneities in the lower mantle

Wentzcovitch

2014

Proc. Natl. Acad. Sci. U.S.A.

109

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“…1), which turned out to be quite similar to the classical geotherms [119,120]. The resulting thermal model [118] of the lower mantle is shown in Fig.…”

Section: Mgsio 3 Perovskitementioning

confidence: 99%

Ab initio theory of planetary materials

Oganov

Price²,

Scandolo³

2005

Zeitschrift Für Kristallographie - Crystalline Materials

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Abstract. Ab initio simulations play an increasingly important role in the studies of deep planetary interiors. Here we review the current state of this field, concentrating on studies of the materials of the Earth's deep interior (MgO--SiO 2 --FeO--Al 2 O 3 , Fe--Si--S--O) and of the interiors of giant planets (H--He system, H 2 O--CH 4 --NH 3 system). In particular, novel phases and phase diagrams, insights into structural and electronic phase transitions, melting curves, thermoelasticity and the effects of impurities on physical properties of planet-forming materials are discussed.

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BurnMan: A lower mantle mineral physics toolkit

Cottaar

Heister

Rose

et al. 2014

Geochem. Geophys. Geosyst.

101

100

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We present BurnMan, an open-source mineral physics toolbox to determine elastic properties for specified compositions in the lower mantle by solving an Equation of State (EoS). The toolbox, written in Python, can be used to evaluate seismic velocities of new mineral physics data or geodynamic models, and as the forward model in inversions for mantle composition. The user can define the composition from a list of minerals provided for the lower mantle or easily include their own. BurnMan provides choices in methodology, both for the EoS and for the multiphase averaging scheme. The results can be visually or quantitatively compared to observed seismic models. Example user scripts show how to go through these steps. This paper includes several examples realized with BurnMan: First, we benchmark the computations to check for correctness. Second, we exemplify two pitfalls in EoS modeling: using a different EoS than the one used to derive the mineral physical parameters or using an incorrect averaging scheme. Both pitfalls have led to incorrect conclusions on lower mantle composition and temperature in the literature. We further illustrate that fitting elastic velocities separately or jointly leads to different Mg/Si ratios for the lower mantle. However, we find that, within mineral physical uncertainties, a pyrolitic composition can match PREM very well. Finally, we find that uncertainties on specific input parameters result in a considerable amount of variation in both magnitude and gradient of the seismic velocities.

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Thermodynamic parameters in the Earth as determined from seismic profiles

Cited by 557 publications

References 40 publications

Spin crossover in ferropericlase and velocity heterogeneities in the lower mantle

Spin crossover in ferropericlase and velocity heterogeneities in the lower mantle

Ab initio theory of planetary materials

BurnMan: A lower mantle mineral physics toolkit

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